Process for making iron sponge pellets containing silicon carbide

ABSTRACT

A process for making iron sponge from iron ores containing at least 95 percent by weight of iron oxide, which comprises pulverizing the iron ore and adding silicon carbide thereto, pelletizing the mixture, and subjecting it to direct reduction. The invention also relates to various uses of the iron sponge so made.

United States Patent [191 Benecke et a1.

[ 1 Aug. 12, 1975 [73] Assignee: Elektroschmelzwerk Kempten GmbH, Munich, Germany 221 Filed: Feb. 25, 1974 21 Appl. No.: 445,413

[30] Foreign Application Priority Data Feb. 23, 1973 Germany 2308888 52 US. Cl. 75/33; 75/3; 75/58 511 int. cl. 0213 13/00 [58] Field of Search 7 5/3, 44 R, 58, 130 R,

[56] References Cited UNITED STATES PATENTS 3,728,107 4/1973 Loricchio 75/130 R 3,765,875 10/1973 Septier et al 75/130 R 2 Primary ExamJinerC. Lovell Assistant ExaminerM. J. Andrews Attorney, Agent, or FirmAl1ison C. Collard [57] r ABSTRACT A process for making iron sponge from iron ores containing at least'95 percent by weight of iron oxide, which comprises pulverizing the iron ore and adding silicon carbide thereto, pelletizing the mixture, and subjecting it to direct reduction. The invention also relates to various uses of the iron sponge so made.

5 Claims, No Drawings PROCESS FOR MAKING IRON SPONGE PELLETS CONTAINING SILICON CARBIDE The present invention relates to a process for making iron sponge from iron ores containing 95 percent or more of iron oxide, for use in producing various types of steels.

Processes are known for melting cast iron with lame]- lar graphite, or with modular graphite, or malleable cast iron, in cupola furnaces, reverberatory furnaces or electric furnaces. To melt these cast irons, a mixture is added in the furnace of cast iron scrap, steel scrap, returns, and pig iron. ln cast iron as well as in steel, and therefore in the scraps of both, a concentration of chemical elements gradually takes place, which are either intentionally alloyed to the commodities during their production for improving their mechanical properties, or which may have been present in the pig iron originating from the ores.

Whle in the conventional, such additives normally do not cause any disturbances, the production of highgrade modular cast irons, or malleable cast iron, prove to be increasingly more difficult. At first, this led to a selection of additives which, however, may be economically unfavorable. The special brands of pig iron needed for modular cast iron and malleable cast iron have to be specially prepared because they have to be of particular technical purity. As scrap steel, on the other hand, such wastes are chosen, which due to their previous use have to be particularly pure, for example, sheets from deep-drawing.

Another known iron used for making high-quality steel is Armco iron, which has been in use for making such high-grade and other steels for a long time.

A material of superior purity is iron sponge. Its impurities are only small quantities of silica, alumina, and traces of calcium and magnesium oxides, which pass into the slag. With regard to the accompanying elements, such as carbon, silicon, manganese, phosphorus and sulfur, only carbon is present. For trace elements, such as copper, titanium, chromium, aluminum, arsenic and lead, only minimal amounts are to be found, for example, less than 0.01 percent by weight in each case.

The fluctuations in the chemical composition of the charge, as well as its different behavior in melting loss depending on the melting process, are balanced by additions, such as ferrosilicon or manganese containing additives. However, an analysis of the variations found with the use of this method do not always come up to recent specifications eg of modular cast iron. By no means can the amount of trace elements be influenced in this manner.

It is the object of the present invention to provide an iron sponge which avoids the shortcomings of the known methods, and a process for producing the iron sponge.

Other objects and advantages of the present invention will become apparent from the following detailed description.

According to the invention, a process has now been found by which iron sponge can be made from iron ores containing 95 percent by weight or more of iron oxide,

in that way that silicon carbide is mixed with the pulvarying chemical composition, e.g. the silicon content, the melts may be used for making, for example, modular cast iron, black-malleable cast, over-eutectoid cast steel, the carbon content of which above 0.9 percent is separated in the raw castings as modular graphite; also other steel brands may be made, e.g. silicon construction steels.

When known iron sponge is added to the melt, the iron sponge having a higher oxygen content as compared to the scraps, an iron-oxide containing slag is formed which causes a severe attack of the acid furnace lining. It is known that due to the especially strong deoxidation effect of silicon carbide, the iron oxide content of the slag scraps are added to the melt is diminished, and the life of the furnace lining is increased. This, 'however, is only true for the existing practice, without addition of iron sponge, because the latter causes a considerable increase in the amount of slag. In order to decrease the iron oxide content of the slag caused by the addition of iron-sponge additional expedient steps have to be taken.

According to the invention, iron oxides are ground to fine grain-size and mixed with equally fine ground silicon carbide, and then made into lumps or pellets in a known manner. Of the iron ores used at least percent should be ground to a size less than 40 82 The silicon carbide is used in an amount of 0.1 10 percent by weight, preferably 0.5 6 percent by weight, calculated on the total amount, and having a grain size of 10 p. 2 mm, preferably 10 ,u, 400 t. This silicon carbide is added in adequate grain size to the iron ore to be pelletized, which after pelletizing, may be roasted and reduced.

The extremely fine distribution of unmeltable silicon carbide in the iron sponge has the effect that, as the latter is melted and silicon carbide is dissolved therein, the distribution in the melt occurs very evenly and the iron oxide entrained in the iron sponge is more readily reduced.

In the known method of adding silicon carbide to the bath, such an evenness in the distribution cannot be brought about as in the above described intimate distribution of e.g. only 2 percent silicon carbide in the iron sponge.

When silicon carbide is introduced into the iron sponge according to the invention, a considerable shortening of the melting-time for each charge, as well as formation of a slag with lower iron content are secured. These two factors, together with the improved life of the furnace lining, provide a considerable advance in this art.

The invention will now be more fully described in a number of examples, but it should be understood that these are given by way of illustration and not by way of limitation.

EXAMPLE 1.

A starting block of 900 kg modular iron was placed into the 3,5 to furnace and covered with reformed material. After melting down, a refill took place with the use of new, clean stacks of sheet until the furnace was filled. Then a substantial specimen of slag was taken off from the surface. After the specimen had cooled down, its weight was 800 g. After grinding, 300 g of mostly spherical metallic occlusions could be drawn out with a magnet. In the balance of 500 g, 16.34 percent Fe and 6.12 percent Mn were found. These figures are within the range of conventional analysis findings in accordance with the common praxis.

EXAMPLE 2.

The melting test of example 1 was repeated while using the same ratios of weight. But instead of the stacks of sheets, 500 kg iron sponge and 0.9 percent of metallurgical silicon carbide, calculated on the total filling of 3.5 to were separately and consecutively added to the melt. In this manner, about 28 kg silicon carbide with about 20 kg pure silicon were introduced, (about 0.55 percent Si). The amount of iron oxide introduced by the sponge iron, is 33 kg. Already to the naked eye the color of the slag showed to be lighter. After cooling, 315 g of slag were weighed, from which only 2 g metallic occlusions could be withdrawn by means of a magnet. The remaining 313 g stag contained 2.73 Fe and 4.54 percent Mn.

EXAMPLE 3.

To a melt from which the slag had been carefully removed, and which weighed 3.5 tons, according to example 1, 1500 kg iron were removed for casting. For replacement, first 900 kg (25 percent) of iron sponge were added to which had been added before the reduction 2 percent of silicon carbide. The remainder was filled up with reformed materials.

The analysis of the added sponge is: 92.2 percent by weight total iron, of which 86.6 percent metallic, 0.7% A1 2.5% SiO 1.0% CaO, 6.7% FeO, corresponding to 5.4% metallic iron, 0.85% C, 2% silicon carbide, (Metallurgical quality 90% SiC). According to the above analysis, the 900 kg iron sponge introduced the following slag-forming compounds: 58 Kg FeO, 23 kg SiO 6.0 kg A1 0 kg CaO, 1.0 kgMgO and, additionally, from the metallurgical silicon carbide, 1 kg SiO The silicon carbide addition is 17 kg with about 12 kg pure silicon.

Theoretically, these 99 kg slag forming compounds are composed of 58% FeO, 23% SiO 6% A1 0 10% CaO, 1% MgO. In reality, the following amounts were found in the slag: 6.0% Fe, corresponding to 8% FeO, 1% Mn, 68% SiO 17% CaO, 12% A1 0 and 1.2% MgO. Instead of the theoretically expected FeO content of 58 percent, the slag contained only 8%. The SiO content derives from the reduction power of the 17 kg silicon carbide resulting in CaO and 25 kg SiO When the amount of 25 kg SiO is added to the introduced 23 Kg SiO the result is 48 kg SiO The amount (by weight) of the slag decreases to 87 kg, due to the FeO removed by reduction. Therefore, the above 48 kg correspond to 55% SiO Added SiO results from the worn furnace lining and adhering sand from the reformed material increase the difference to 68 percent.

While the process of the present invention has been described mainly in respect to only a few specific examples for purposes of a complete and detailed disclosure, it will be readily apparent to those skilled in the art that many other embodiments and modifications are within the purview of this invention. Accordingly, the instant invention should not be construed as limited in any particulars except as recited in the appended claims or required by the prior art.

What is claimed is:

1. A process for making iron sponge from iron ores containing at least 95% by weight of iron oxide comprising, pulverizing the iron ore to extremely fine grain size, mixing the pulverized iron ore with fine-grained silicon carbide, pelletizing the so obtained mixture, and subjecting the same to direct reduction.

2. The process according to claim 1 wherein the silicon carbide is mixed with the pulverized iron ore in a grain size approximately corresponding to the grain size of the iron ore, the obtained mixture is pelletized and the obtained pellets are sintered.

3. The process according to claim 1 wherein at least percent by weight of iron ores are used having a grain size less than 40 ,u..

4. The process according to claim 3 wherein silicon carbide is used in an amount of 0.1-10 percent by weight calculated on the total weight and in a grain size between 10 p. and 2mm.

5. The process according to claim 4 wherein silicon carbide is used in an amount of 0.5 6 percent by weight calculated on the total weight and in a grain size of 10 p. to 400 11.. 

1. A PROCESS FOR MAKING IRON SPONGE FROM IRON ORES CONTAINING AT LEAST 95% BY WEIGHT OF IRON OXIDE COMPRISING, PULVERIZING THE IRON ORE TO EXTREMELY FINE GRAIN SIZE, MIXING THE PULVERIZED IRON ORE WITH FINE-GRAINED SILICON CARBIDE, PELLETIZING THE SO OBTAINED MIXTURE, AND SUBJECTING THE SAME TO DIRECT REDUCTION.
 2. The process according to claim 1 wherein the silicon carbide is mixed with the pulverized iron ore in a grain size approximately corresponding to the grain size of the iron ore, the obtained mixture is pelletized and the obtained pellets are sintered.
 3. The process according to claim 1 wherein at least 80 percent by weight of iron ores are used having a grain size less than 40 Mu .
 4. The process according to claim 3 wherein silicon carbide is used in an amount of 0.1-10 percent by weight calculated on the total weight and in a grain size between 10 Mu and 2mm.
 5. The process according to claim 4 wherein silicon carbide is used in an amount of 0.5 - 6 percent by weight calculated on the total weight and in a grain size of 10 Mu to 400 Mu . 